At the present time, commercially available high efficiency photovoltaic devices, or solar cells, as they are also known, are constructed by diffusing a suitable impurity into a single crystal base material to produce a p-n junction near the surface of the base to which illumination is to be applied, and in a plane parallel to said surface. The depth of the diffusion and the concentration of impurity atoms diffused are determined by trade-offs between the sheet resistance of the diffused layer and the optical absorption characteristics of the base material. These values will vary depending upon the particular material utilized for the single crystal base.
High efficiency cells of this type now in conventional use usually embody a single crystal silicon base, in which case it has been found that the depth of the diffusion preferably is about one micron, and the concentration of impurity atoms diffused is approximately 10.sup.19 /cc. High efficiency cells of this type are used extensively for primary power production on space flights, since these cells have virtually infinite lifetimes with negligible performance degradation.
The main problem that exists in using solar cells of this type for large scale earth-based power systems has been the high cost of producing the single crystal wafers used as the starting material for cell production. For example, it has been found that the cost of solar cell power supplies for space applications has been estimated at $100.00 to $200.00 per watt, while the least expensive earth-based power supplies using single crystal silicon cells has been estimated as being in the neighborhood of $40.00 to $60.00 per watt. However, it has been estimated that to be financially competitive with atomic power, photovoltaic power supplies should not exceed an approximate cost of fifty cents per watt.
It is therefore a primary object of the present invention to eliminate the need for using single crystals as the starting material for high efficiency solar cell production. By eliminating this requirement, it is estimated that the cost per cell can be reduced 100 times. In addition, the present invention simplifies the manufacturing procedure presently being used in connection with high efficiency solar cells by eliminating the standard diffusion process that is used for forming the rectifying junction, thus further reducing the cost of the cell.
Other objects, features and advantages of the invention will become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.